A compressor serves to compress air, and an important application thereof is the use in a turbocharger. A turbocharger compresses the air flowing into an engine in order to supply more air into a cylinder. In this way, more fuel can be added so that more power can be obtained from a cylinder compared to a case in which no turbocharger is used.
A turbocharger is constituted by a compressor and a turbine, which is rotated by exhaust gas of the engine. The turbine, i.e., the turbine wheel is connected to the compressor wheel by a shaft. Hence, the rotation of the turbine drives the compressor, which in turn compresses ambient air supplied thereto and feeds it to the cylinder(s) of the engine.
A main problem with turbochargers is that they do not provide an immediate power boost when it is requested, e.g., by operating an accelerator pedal in a vehicle. Namely, it takes some time for the turbine to reach the necessary speed before a boost can be produced. This time length is also referred to as “turbo lag”.
As a measure for handling this problem it has been proposed to employ an auxiliary electric machine, by which the turbocharger is assisted in supercharging the engine. Moreover, the electric machine, when arranged as a motor/generator, may also be used to charge a battery or directly supply power to electrical consumers. For example, document U.S. Pat. No. 5,406,797 describes such a turbocharger, in which a rotary electric machine is used, which may be a squirrel cage induction machine.
However, for a turbocharger high speeds are necessary, which may reach up to 250 kRPM. That is, the electric machine and a corresponding electronic controller for the electric machine must have high speed capability. In addition, a high low end torque, a high overall efficiency should be achieved, and the components should also comply with a high temperature environment.
In addition, in case a mass production is intended, a low cost solution is mandatory, in particular for the electronic controller.
Another possibility to improve the turbolag issue is to add an electrically driven compressor in serial (before or after a standard turbocharger). In that case, constraints on motor design are very similar, but for the speed which is lower (120 kRPM).
Therefore, the present application is directed to driving a turbocharger or an electrically driven compressor (also called electric boosting system) with an electric motor, using, e.g., a vehicle electric network.